From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLACK, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7B726C433E3 for ; Wed, 1 Jul 2020 15:29:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6A5E5207D0 for ; Wed, 1 Jul 2020 15:29:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731986AbgGAP3z (ORCPT ); Wed, 1 Jul 2020 11:29:55 -0400 Received: from mga07.intel.com ([134.134.136.100]:27246 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731622AbgGAP3y (ORCPT ); Wed, 1 Jul 2020 11:29:54 -0400 IronPort-SDR: u12ehlGk2bZD2+A79AS0I94QhNN2Eh0SgqbDX7H3RiOwt1tXQLsEAIXNl1T+zbIPQW9eMayYSI 2XhUw2Nqb0uw== X-IronPort-AV: E=McAfee;i="6000,8403,9668"; a="211664191" X-IronPort-AV: E=Sophos;i="5.75,300,1589266800"; d="scan'208";a="211664191" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Jul 2020 08:29:53 -0700 IronPort-SDR: MATPxC2NxKlfAgUDaGpHd5kBCQSE7i0usf4jUnqYf9Kqooj4xzplQR/F0CEfB8wloMMj/uwBQ+ 6nCJR6paZMvw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,300,1589266800"; d="scan'208";a="295592133" Received: from viggo.jf.intel.com (HELO localhost.localdomain) ([10.54.77.144]) by orsmga002.jf.intel.com with ESMTP; 01 Jul 2020 08:29:53 -0700 Subject: [PATCH 1/3] mm/vmscan: restore zone_reclaim_mode ABI To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Dave Hansen , ben.widawsky@intel.com, alex.shi@linux.alibaba.com, dwagner@suse.de, tobin@kernel.org, cl@linux.com, akpm@linux-foundation.org, ying.huang@intel.com, dan.j.williams@intel.com, cai@lca.pw, stable@vger.kernel.org From: Dave Hansen Date: Wed, 01 Jul 2020 08:26:23 -0700 References: <20200701152621.D520E62B@viggo.jf.intel.com> In-Reply-To: <20200701152621.D520E62B@viggo.jf.intel.com> Message-Id: <20200701152623.384AF0A7@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen I went to go add a new RECLAIM_* mode for the zone_reclaim_mode sysctl. Like a good kernel developer, I also went to go update the documentation. I noticed that the bits in the documentation didn't match the bits in the #defines. The VM never explicitly checks the RECLAIM_ZONE bit. The bit is, however implicitly checked when checking 'node_reclaim_mode==0'. The RECLAIM_ZONE #define was removed in a cleanup. That, by itself is fine. But, when the bit was removed (bit 0) the _other_ bit locations also got changed. That's not OK because the bit values are documented to mean one specific thing and users surely rely on them meaning that one thing and not changing from kernel to kernel. The end result is that if someone had a script that did: sysctl vm.zone_reclaim_mode=1 That script went from doing nothing to writing out pages during node reclaim after the commit in question. That's not great. Put the bits back the way they were and add a comment so something like this is a bit harder to do again. Update the documentation to make it clear that the first bit is ignored. Signed-off-by: Dave Hansen Fixes: 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE") Cc: Ben Widawsky Cc: Alex Shi Cc: Daniel Wagner Cc: "Tobin C. Harding" Cc: Christoph Lameter Cc: Andrew Morton Cc: Huang Ying Cc: Dan Williams Cc: Qian Cai Cc: Daniel Wagner Cc: stable@vger.kernel.org --- b/Documentation/admin-guide/sysctl/vm.rst | 10 +++++----- b/mm/vmscan.c | 9 +++++++-- 2 files changed, 12 insertions(+), 7 deletions(-) diff -puN Documentation/admin-guide/sysctl/vm.rst~mm-vmscan-restore-old-zone_reclaim_mode-abi Documentation/admin-guide/sysctl/vm.rst --- a/Documentation/admin-guide/sysctl/vm.rst~mm-vmscan-restore-old-zone_reclaim_mode-abi 2020-07-01 08:22:11.354955336 -0700 +++ b/Documentation/admin-guide/sysctl/vm.rst 2020-07-01 08:22:11.360955336 -0700 @@ -948,11 +948,11 @@ that benefit from having their data cach left disabled as the caching effect is likely to be more important than data locality. -zone_reclaim may be enabled if it's known that the workload is partitioned -such that each partition fits within a NUMA node and that accessing remote -memory would cause a measurable performance reduction. The page allocator -will then reclaim easily reusable pages (those page cache pages that are -currently not used) before allocating off node pages. +Consider enabling one or more zone_reclaim mode bits if it's known that the +workload is partitioned such that each partition fits within a NUMA node +and that accessing remote memory would cause a measurable performance +reduction. The page allocator will take additional actions before +allocating off node pages. Allowing zone reclaim to write out pages stops processes that are writing large amounts of data from dirtying pages on other nodes. Zone diff -puN mm/vmscan.c~mm-vmscan-restore-old-zone_reclaim_mode-abi mm/vmscan.c --- a/mm/vmscan.c~mm-vmscan-restore-old-zone_reclaim_mode-abi 2020-07-01 08:22:11.356955336 -0700 +++ b/mm/vmscan.c 2020-07-01 08:22:11.362955336 -0700 @@ -4090,8 +4090,13 @@ module_init(kswapd_init) */ int node_reclaim_mode __read_mostly; -#define RECLAIM_WRITE (1<<0) /* Writeout pages during reclaim */ -#define RECLAIM_UNMAP (1<<1) /* Unmap pages during reclaim */ +/* + * These bit locations are exposed in the vm.zone_reclaim_mode sysctl + * ABI. New bits are OK, but existing bits can never change. + */ +#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ +#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ +#define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */ /* * Priority for NODE_RECLAIM. This determines the fraction of pages _